1. Field of the Invention
The present invention relates generally to a process for etching a copper containing metallic film and a process for forming wiring of a copper containing metal in semiconductor devices.
2. Description of the Background Art
Generally, aluminum containing metallic materials have been used for metallic wiring in semiconductor devices, such as ULSI and VLSI devices. As semiconductor devices become more and more minute, the sizes of metallic wiring, required by the design rules for such devices, become smaller than 0.5 .mu.m. However, in a case where an aluminum containing metal is used for wiring, if the size thereof becomes smaller than 0.5 .mu.m, it is known that the reliability of wiring decreases. In addition, the aspect ratio of wiring becomes a relatively great value, and it therefore becomes difficult to perform flattening of an insulation film thereafter.
In recent years, attention has been given to wiring of a copper containing metal on the following grounds, in addition to the aforementioned disadvantage in wiring of aluminum containing metal. That is, the electrical resistance of Cu (about 1.4 .mu..OMEGA..cm) is smaller than that of Al (about 2.8 .mu..OMEGA..cm), and copper containing metallic film can be made thinner than aluminum containing metallic film, even if both widths thereof are the same.
Various processes for etching such a copper containing metallic film to form metallic wiring have been proposed. One of such processes is disclosed in Japanese Patent Second (examined) Publication (Tokko Sho.) No. 61-40757. In this process, etching of a copper containing metallic film is performed by a glow discharge in an organic gas atmosphere, which organic gas contains methyl/methylene groups, while a temperature of the copper is maintained in a range of 40.degree. to 200.degree. C. Another process is disclosed in Lecture Paper 1p-L-1 of the Japanese Applied Physical Society in the spring of 1989 ("High-Temperature RIE of Cu Wiring"). In this process, etching of a copper containing metallic film is performed at a high temperature greater than 350.degree. C. by means of chlorine gases, e.g. Cl.sub.2 or CCl.sub.4, and nitrogen gas (N.sub.2). Another process is disclosed in Japanese Patent First (unexamined) Publication (Tokkai Hei.) No. 1-234578. In this process, by adding hydrogen (H.sub.2) to an etching gas while maintaining the same at a high temperature, a slightly etchable copper oxide is reduced so as to enable dry etching of a copper containing metallic film. A further process is disclosed in Japanese Patent First (unexamined) Publication (Tokkai Sho.) No. 63-12138. In this process, patterning of a copper containing metallic film is performed by way of a so-called ion milling method by irradiating neutral particles on the copper film.
The aforementioned etching processes are performed at a high temperature except for the process of Japanese Patent First (unexamined) Publication (Tokkai Sho.) No. 63-12138. In the processes performed at a high temperature, there are disadvantages in that it is difficult to maintain uniformity of thermal distribution in the substrate having the copper containing metallic film, and that the surface of the copper containing metallic film tends to become oxidized. On the other hand, since the process of Japanese Patent First (unexamined) Publication (Tokkai Sho.) No. 63-12138 uses a mask made of SiO.sub.2. TiN or the like as a protective film in order to prevent oxidization of the copper containing metallic film, this process is quite practical to use. However, in this process, in a case where a barrier metal layer is used as a foundation of the copper containing metallic film, two etching steps must be used, one of which is a sputter etching step for the copper containing metallic film by means of, e.g. an ion milling apparatus, and the other of which is an etching step of the barrier metal layer by way of reactive ion etching which uses fluorine (F) radicals. This means increased man-hours are required for carrying out the process.